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KentuckyFC writes "The universe today is filled with beautiful spiral galaxies — but it hasn't always been this way. In the early universe, there were no spiral galaxies, raising an interesting question: when did galaxies get their spirals, and how did they emerge? Now astronomers have the answer, thanks to an analysis of galaxies in an image taken by the Hubble Space Telescope known as the Ultra Deep Field. This shows some 10,000 galaxies of various ages. By ordering a subset of these by type and by age, astronomers have worked out how and when spirals must have evolved. It turns out the first spiral galaxies were simple two-armed structures and appeared when the universe was about 3.8 billion years old. But they say the universe had to wait until it was 8 billion years old before more complex multi-armed galaxies emerged, like the Milky Way and Andromeda."

We are a creation of a second generation star. With our heavier elements that are assumed to be a product of the first generation stars dying process.Assuming most Stars last an average of 10 billion years. It would be save to assume the second generation started 8 billion years after the big bang. Now creating of these heavier elements probably made gravity distribution in the galaxy a little less consistent creating new shapes too.

If I'm remembering my astronomy correctly, first generation stars were much larger and faster rotating, but also much shorter-lived in general - some had lifespans possibly as short as a few million years.

I thought it was third generation? Did something new get discovered while I wasn't looking?

And as SJHillman pointed out correctly, first generation (Pop3 [wikipedia.org]) stars were (allegedly, we still didn't see a single one of them) almost entirely H and He, insanely huge and existed for just a few million years (compared to the billions of years that contemporary stars have... provided they ain't too big).

So I'd say we're probably orbiting one of the first stars that have enough metal to have "rock" planets and hence

Earth formed from heavy elements produced in at least one prior generation star, but there could be more than just one prior generation (It's very, very unlikely that all or nearly all the medium weight elements above lithium, in our solar system, came from just one older star, and pretty unlikely even that all the heavies above Iron were cooked up in just one supernova).
It's not a safe assumption that stars last an average of 10 Billion years. The most numerous types, red dwarfs, make up 80-90% of all stars, last a lot longer than that, and probably stay stable on the main sequence for 100-200 billion years (American Billions). They also shouldn't spread elements around much when they finally do leave the main sequence. Stars about the size of our Sun, spectral class G2, typically live about 10 Billion years, but make up only about 2% of stars. Big stars, type O, B, and A, burn more quickly, and it's possible to get enough hydrogen together for a star to burn through all its fuel and supernova in mere hundreds of thousands of years, or possibly even a blazing fast 10's of thousands. Those stars are rare, but they are so massive that even a few produce enough heavy elements and push enough gas around when they supernova, to create hundreds of sun sized and smaller stars and all the heavy elements to give such stars the solid, rocky planets we now think are practically ubiquitous.
The supernova explosions are a common source for two effects - heavy element formation, and compressive shock waves that trigger new stars forming in nearby interstellar gas clouds. Many of these gas clouds are already enriched with heavy metals from previous supernovae, Spiral galaxies tend to get regions of new star formation, and quiet regions. But, the high and low density regions in spirals like our Milky Way exist on larger scales than the star forming "nursery" clouds, and this is largely because gas clouds are not just compressed by novae - both the dense star forming clouds and very large but more difuse clouds colide with other clouds, including clouds that were part of dwarf galaxies being captured by the big spirals. So, it's a partial coincidence - Older generation stars have some influence on the shapes of spiral galaxy features, but dwarf galaxy capture has more, and the rare colisions of spirals with other big galaxies show just how much influence the large scale objects can have, producing wildly twisted galaxys such as

If anyone wants to read up on this sort of thing, please remember, because astronomers named them before they knew anything about why there were multiple distinct types of stars in the same mass ranges, Population II stars are actually older than Population I, and Population III older than II. A given population usually includes multiple generations of stars. As an exception, the very oldest, massive stars that novaed within the first million years or so after star formation began, and produced so many heavy elements are called Population III, and most probably represent just a single generation and possibly only the largest types.

The comment was perfectly on-topic if you understood it. It summarizes the main theme of a trilogy of books: the human mind is better at spotting patterns than the universe is at creating them. So if something seems like an unlikely coincidence, the best assumption is that it is an unlikely coincidence, unless you can hypothesize a reasonable mechanism to explain the connection (and then make successful predictions using that).

Jesus was bored, flicked a couple of galaxies with his finger and thought it looked cool, so he did it to them all. He started making them look crazier and crazier until God told him to cut it out, or else.

When the gods rotate the universe to look for their next vacation spot, the resulting Coriolis force makes galaxies spin. They don't all spin in the same direction because of The Great Nebula Outing Debate of 10 000 000 000 PBB (Post-Big-Bang), when the Almighty-Mothers-In-Law kept rotating back and forth until The-So-Cute-One (then a toddler at barely 10000 years old) randomly sneezed a few more stars on Orion.Ever since that event, people on Durandil Major have been unable to predict the way the water will flow when they flush their toilets.

The Elmegreens examined 269 spirals in the Hubble Ultra Deep Field and discarded all but 41 because of factors such as an inability to discern a clear spiral structure or the lack of redshift data which gives a galaxy’s age.

They divided these 41 spiral galaxies into five different types, based on features such as the number and clarity of arms, whether well-defined or clumpy and so on.

It sounds like they only found a few of each type, seems more like a good hypothesis than "the answer". It also makes you wonder if they cherry picked some of their data.

The Elmegreens examined 269 spirals in the Hubble Ultra Deep Field and discarded all but 41 because of factors such as an inability to discern a clear spiral structure or the lack of redshift data which gives a galaxyâ(TM)s age.

They divided these 41 spiral galaxies into five different types, based on features such as the number and clarity of arms, whether well-defined or clumpy and so on.

It sounds like they only found a few of each type, seems more like a good hypothesis than "the answer". It also makes you wonder if they cherry picked some of their data.

1. You throw out all non-spirals: not relevant.2. You throw out proto-spirals where there's mushy arm-sh structures: potential bias, yes but2a. You also throw out other spirals where you cannot objectively classify them as grand (2) or multi-armed (>2) spirals or... to one of the five types -- not an inherent time bias.3. You throw out all data where you have no redshift to determine age: potential bias, yes but3a You're attempting to determine a relationship with age. If you have no age data, how is that cherry picking?

There is a difference between objectively screening data based on logical considerations and cherry picking. Cherry picking typically involves biased selections or the use of supposedly objective selection criteria to obtain a directed result. I say supposedly because the true objectivity depends upon how the selection criteria actually relate to the hypothesis or analytical method.

As for the rest, I don't see how the paper claims to have "the answer." You're also incorrect that it's a good hypothesis -- the hypothesis is what you test against the data, not the conclusion that your observations are consistent with the hypothesis. They have a decent conclusion of consistency. Now they could use independent confimation, hopefully with a larger population of samples.

Don't know, but scuzzlebutt posted an interesting link [cornell.edu] further up, at which you can read:

Scientists believe that on large scales the Universe is isotropic (the same in all directions). Thus, from our perspective, half of all spiral galaxies should spin clockwise, and half counter-clockwise. A recent analysis of the spin of spiral galaxies confirms this. The public classified over 35,000 spiral galaxies with spins both clockwise and counter-clockwise in the Sloan Digital Sky Survey as part of the Galaxy Zoo project.

Retrospectively it could have been guessed long ago that disk galaxies need at least a few tens of rotation periods to look progressively like symmetric accretion disks in other astrophysical contexts (disks around black-holes, stars or planets). The difference between galaxies and smaller disks is mainly the number of rotations they could make, a few tens of rotations for spiral galaxies, millions or billions for smaller disks.

The mathematics governing many physical phenomena is strikingly similar. Its the frequency and wavelength that make them look radically different. Heat dissipation due to day/night cycles through a structure looks a lot like microwave attenuation in a surface. Same math, different time scale.

It also makes one wonder if the eventual form of a galaxy will resemble a planetary disc, with a bunch of large bodies (black holes?) orbiting a really big central one, surrounded by largely empty space.

Predictions of rotation speed of stars towards the edges of galaxies do not agree with Keplerian predictions used to predict the orbital speed of planets around our sun. So either gravity doesn't behave the same in the outer parts of galaxies as it behaves around our sun, or (the hypothesis) there is some other mass that we can't see (dark mass). Right now, what we know is that observations don't match predictions based on the math that works for our solar system's planets.

Thanks, that helped me understand support for dark matter as well. For clarification though, would it be fair to say that we do use the same math and when the answer didn't fit our prediction, we didn't change the math, but rather assumed the math is right and that we must not be able to observe all of the mass?

Also not necessarily consistent with the observation of the effects of gravity on light passing by clusters of galaxies, and the fact that galaxies appear to be accelerating away the further the galaxy appears to be.

This does not mean that our theory of gravity isn't wrong on large scales, and perhaps dark matter and dark energy do not have the level of influence that our current theory projects, but we are seeing effects that essentially suggest that there is something like anti-gravity working across very

Think about the 'closed model' of the universe. The one that says space-time is closed on itself like the surface of a balloon and if you shot a beam of light into space, eventually it would loop around and hit you in the ass (sorry for the overly technical terminology).

Gravity would work around this curve as well. The force that would decelerate two galaxies moving apart would be counteracted by a (much smaller) force of the two galaxies attracting each other around the longer route of the closed curve.

Probably because gravity (the gravitational constant) will turn out not to be scale invariant.

Dark matter/dark energy might work as explainers for expansion of the universe and rotational velocities of parts of galaxies. But once that theory is accepted, one will have to explain why dark whatever doesn't seem to affect planetary motions and someone dropping cannon balls off a tower.

This is the only post so far that mentions dark matter. Without dark matter, the galaxy spirals should be much less rigid. Did the old galaxies with two arms also reveal the presence of dark matter, so that its presence has been constant throughout the age of the universe? Or do they just ignore dark matter and treat it as a given that stars at the edge of galaxies orbit at the same speed as stars closer in, unlike our solar system with its gravity constraints?

From looking at TFA what I garner is that galaxies got arms a long time ago "as they got older". Specifically: "Then the clumps elsewhere in the glalxy (sic) begin to smear out forming woolly, indistinct arms." Nailing down the process, they follow with "More complex structures follow later." Wow, mystery solved.
Now I seem to remember some research 10 or so years ago that showed through computer simulations that 2 galaxies composed of homogeneous distributions of stars, if they pass relatively close to eac